Epoxy encapsulating and lamination adhesive and method of making same

ABSTRACT

An adhesive includes an epoxy resin and a hardener. The hardener includes trioxdiamine, diaminodicyclohexylmethane, toluene diamine, and bisphenol-A dianhydride.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate generally to structures and methodsfor packaging semiconductor devices and, more particularly, to asemiconductor device package adhesive that provides stable high voltageelectrical operation.

As integrated circuits become increasingly smaller and yield betteroperating performance, packaging technology for integrated circuit (IC)packaging has correspondingly evolved from leaded packaging tolaminated-based ball grid array (BGA) packaging and eventually to chipscale packaging (CSP). Advancements in IC chip packaging technology aredriven by ever-increasing needs for achieving better performance,greater miniaturization, and higher reliability. New packagingtechnology has to further provide for the possibilities of batchproduction for the purpose of large-scale manufacturing thereby allowingeconomy of scale.

Some semiconductor devices and packages include high voltage powersemiconductor devices that are used as switches or rectifiers in powerelectronic circuits, such as switched mode power supplies, for example.Most power semiconductor devices are only used in commutation mode(i.e., they are either on or off), and are therefore optimized for this.Many power semiconductor devices are used in high voltage powerapplications and are designed to carry a large amount of current andsupport a large voltage.

In use, some high voltage power semiconductor devices are connected toan external circuit by way of a power overlay (POL) packaging andinterconnect system, with the POL package also providing a way to removethe heat generated by the device and protect the device from theexternal environment. A standard POL manufacturing process typicallybegins with placement of one or more power semiconductor devices onto adielectric layer by way of an adhesive. Metal interconnects (e.g.,copper interconnects) are then electroplated onto the dielectric layerto form a direct metallic connection to the power semiconductordevice(s). The metal interconnects may be in the form of a low profile(e.g., less than 200 micrometers thick), planar interconnect structurethat provides for formation of an input/output (I/O) system to and fromthe power semiconductor device(s).

Inherent to some packaging technologies is the use of high-voltageswitches or assemblies typically having a length of five centimeters ormore. Typically such switches include a trapezoidal cross-section orprofile that is affixed to a base or supporting material such as kapton,then electrically connected to other components within an assembly. Thetrapezoidal cross-section includes a pair of parallel surfaces, and apair of non-parallel surfaces that are opposite one another. Typically,one of the parallel surfaces includes a surface of switches that isadhered to, for instance, the kapton, and the other of the parallelsurfaces includes a ground or power plane.

In order to avoid warpage and protect the high-voltage assembly fromexternal influences, an encapsulant is often applied, which is thenlaser ablated in order to electrically connect to the ground or powerplane. However, because of thermal effects, water absorption, and thelike, such an assembly is prone to warpage. Further, because theencapsulant also typically includes voids or may be applied either toothinly or too thickly, corona discharge and sparking can occur duringhigh-voltage operation, which can lead to performance degradation andearly life failure.

And, with respect to providing dielectric isolation between the anodeand cathode junctions, a high dielectric material that is capable ofproviding a high reverse breakdown voltage (e.g., up to 10 kV) istypically provided for the semiconductor diode. However, such dielectricmaterials often have an increased thickness that may be incompatiblewith certain POL packaging techniques for the semiconductor diode and,if the thickness is not properly controlled, can lead to increasedparasitic inductance.

Accordingly, there is a need for a simplified method for encapsulatinghigh-voltage switches and assemblies, and for an improved adhesive.

BRIEF DESCRIPTION OF THE INVENTION

The invention is an epoxy encapsulating and lamination adhesive andmethod of making same.

In accordance with one aspect of the invention, an adhesive includes anepoxy resin and a hardener. The hardener includes trioxdiamine,diaminodicyclohexylmethane, toluene diamine, and bisphenol-Adianhydride.

In accordance with another aspect of the invention, a method ofpreparing an adhesive includes mixing together a plurality of reactantsto form a hardener, the reactants comprising trioxdiamine,diaminodicyclohexylmethane, toluene diamine, and bisphenol-Adianhydride, mixing the hardener with an epoxy resin to form an uncuredadhesive mixture, and curing the uncured adhesive mixture.

In accordance with yet another aspect of the invention, a method offorming a semiconductor device package includes positioning asemiconductor device against a material to form a space between asurface of the semiconductor device and the material, mixing together aplurality of reactants to form a hardener, the reactants comprisingtrioxdiamine, diaminodicyclohexylmethane, toluene diamine, andbisphenol-A dianhydride, mixing the hardener with an epoxy resin to forman uncured adhesive mixture, placing the uncured adhesive mixture intothe space, and curing the uncured adhesive mixture.

Various other features and advantages will be made apparent from thefollowing detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate preferred embodiments presently contemplated forcarrying out the invention.

In the drawings:

FIG. 1 is a schematic cross-sectional side view of a semiconductordevice package using an adhesive/encapsulant that is formulated andprepared according to an embodiment of the invention.

FIGS. 2-13 are schematic cross-sectional side views of a semiconductordevice package during various stages of a manufacturing/build-up processthat can benefit from embodiments of the invention.

FIG. 14 is a flowchart illustrating a method of preparing anadhesive/encapsulant according to an embodiment of the invention.

FIG. 15 is a flowchart illustrating a method of preparing an epoxyadhesive and/or molding encapsulant.

DETAILED DESCRIPTION

Embodiments of the invention provide for an adhesive/encapsulant for asemiconductor device package having a high breakdown voltage and lowparasitic inductance, as well as a method of forming such asemiconductor device package. The formulation for theadhesive/encapsulant meets certain requirements that include but are notlimited to low viscosity, ability to partial cure, low surface tension,low stress, working life, gelling at room temperature, ability to laserablate at a desired laser wavelength, ability to obtain and control adesired glass transition temperature, and good dielectric properties.The semiconductor device package is manufactured such that edges of thesemiconductor device are passivated using multiple dielectric layers ofdiffering thickness, with an electrical interconnect system being formedto top and bottom surfaces of the semiconductor device.

Referring to FIG. 1, a semiconductor device package 10 is shown thatincorporates an exemplary embodiment of the invention. The semiconductordevice package 10 includes a semiconductor device 12 therein that may bein the form of a die, diode, or other electronic device. Semiconductordevice 12 is in the form of a high voltage semiconductor diode, such asan optical diode having a back bias in the reverse direction, forexample. As shown in FIG. 1, semiconductor device 12 may have atrapezoidal shape, however, it is recognized that other shapes andconfigurations for semiconductor device 12 are envisioned, such as arectangular shape, for example. Furthermore, regarding the shape andsize of semiconductor device 12, it is recognized that semiconductordevice 12 is in the form of a “thicker” device, with semiconductordevice 12 having a thickness/height of up to 40 mm or more, for example.

The semiconductor device 12 includes a substrate 14 formed of asemiconductor material such as silicon, silicon carbine, galliumnitride, gallium arsenide, or another semiconductor material, that hasimpurities added to it to create a region on one side that containsnegative charge carriers (electrons), called n-type semiconductor, and aregion on the other side that contains positive charge carriers (holes),called p-type semiconductor. The boundary within the substrate betweenthese two regions, called a PN junction, is where the action of thediode takes place, with the substrate conducting conventional current ina direction from the p-type side (i.e., the anode) to the n-type side(i.e., the cathode), but not in the opposite direction. Semiconductordevice 12 is termed as a “high voltage” device in that it will typicallybe operated at a voltage of 3 kV or greater, with voltages above 10 kVbeing envisioned.

Formed on the substrate, and attached to each of the P and N regions, isa plurality of metalized circuits and/or connection pads (i.e.,terminals) 16 through which an electrical connection can be made tosemiconductor device 12. As shown in FIG. 1, the circuits/connectionpads 16 are formed on surfaces 18, 20 of substrate, such that electricalconnections can be made with two surfaces of semiconductor device 12.

Also included in semiconductor device package 10 is a first passivationor dielectric layer 22 that is formed about surfaces 18, 20 and theedges 24 of the semiconductor device 12, so as to cover substrate 14 andmetalized circuits/connection pads 16. First passivation layer 22 is inthe form of a high performance film, such as silicon nitride, siliconoxide, or another suitable dielectric material that may include anadhesive that is formed according to an embodiment of the invention,that is applied onto semiconductor device 12 so as to have a uniformthickness. According to one embodiment of the invention, the firstpassivation layer 22 is applied using plasma enhanced chemical vapordeposition (PECVD) so as to have a thickness in the order of 1-2microns. The first passivation layer 22 thus serves to passivate theedges 24 of semiconductor device 12 as well as protect the surfaces ofsubstrate 14 and metalized circuits/connection pads 16, such as duringmanufacturing processing steps of the semiconductor device package 10(e.g., etching, lamination, etc.), as explained in detail below.

As shown in FIG. 1, portions of first passivation layer 22 are removedin locations adjacent metal circuits/connection pads 16 of semiconductordevice 12, such as by using reactive ion etching (RIE), so as to providefor an electrical interconnection to made to those circuits/connectionpads 16. According to an embodiment of the invention, wheresemiconductor device package 10 is in the form of an optically activedevice, first passivation layer 22 is optically clear, so as to permitlight to pass there through while still offering protection of anoptical window 28 of the semiconductor device package 10. However, it isrecognized that semiconductor device 12 may be in the form of adevice/diode that is not an optically active device, and thusillustrated embodiments may not include an optical window 28, norrequire use of an optically clear passivation layer.

While the first passivation layer 22 serves to passivate the edges 24 ofsemiconductor device 12 and provide a protective covering for the metalcircuits/connection pads 16 formed thereon, it is recognized that thethinness of the first passivation layer 22 (i.e., the coating of siliconnitride/oxide) may, nevertheless, be insufficient to hold very largevoltages. As such, semiconductor device package 10 may also include asecond passivation or dielectric layer 30 that is applied on top of thefirst passivation layer 22 and that extends out over the edges 24 ofsemiconductor device 12, with an adhesive layer (not shown) beingoptionally included there between depending on the form of the secondpassivation layer 30. As shown in FIG. 1, the second passivation layer30 is applied as a thicker layer or coating of dielectric material ascompared to first passivation layer 22, so as to provide a higherdielectric strength and increase the breakdown voltage of semiconductordevice package 10. The thickness of second passivation layer 30 may beup to 1-2 mm, according to one embodiment of the invention, and may alsobe formed of an adhesive that is formed according to embodiments of theinvention.

Since the nitrides and oxides used for forming first passivation layer22 often cannot be applied much thicker than a few microns, secondpassivation layer 30 may be formed of the same material or a differentmaterial than first passivation layer 22, i.e. one that provides goodcompatibility (i.e., adhesion) to the already applied nitride/oxide filmof the first passivation layer 22. Second passivation layer 30 may thusbe formed of such materials as polyimides, epoxies, paralyene,silicones, etc. Second passivation layer 30 may be in the form of apre-formed laminate sheet or film that is formed of Kapton®, Ultem®,polytetrafluoroethylene (PTFE), Upilex®, polysulfone materials (e.g.,Udel®, Radel®), or another polymer film, such as a liquid crystalpolymer (LCP) or a polyimide material. According to an embodiment of theinvention, second passivation layer 30 is formed using an epoxy resinthat is cured using an amine-imide hardener that is described below inFIG. 14. Alternatively, second passivation layer 30 can be in liquidform and applied via one of a spray coating application, a moldingprocess, or a selective deposition process (i.e., “direct writing”), aswill be explained in detail below. Whether second passivation layer 30is formed of dielectric material applied in laminate form, liquid form,or a combination thereof, the second passivation layer 30 is appliedover the edges 24 of the semiconductor device 12 in a controlled mannersuch that the thickness thereof is sufficient for a desired/requireddielectric strength but yet does not excessively increase the inductiveloop of the semiconductor device 12. A typical thickness of secondpassivation layer 30 is thus, for example, in the range of around 10-50microns for every 1000 volts of dielectric breakdown strength needed.

Thus, first passivation layer 22 may include nitrides, oxides, or otherknown dielectrics to provide an improved dielectric strength, and may beformed of an adhesive/encapsulant that is formed according toembodiments of the invention. Second passivation layer 30 may be formedof the same material. As such, according to the invention, either orboth layers 22, 30 may be formed of an adhesive/encapsulant that isformed according to embodiments of the invention.

As further shown in FIG. 1, according to one embodiment of theinvention, a base dielectric layer 42 is applied to surface 18 ofsemiconductor device 12, such that a thicker dielectric layer is formedentirely about the semiconductor device (i.e., combination of secondpassivation layer 30 and layer 42 is formed about semiconductor device12). According to one embodiment, dielectric layer 42 is formed of anadhesive/encapsulant that is formed according to embodiments of theinvention. Each of the first and second passivation layers 22, 30, aswell as the base dielectric laminate and an additional laminate sheet ofdielectric film 38 secured to base dielectric laminate 42, areselectively patterned to form a plurality of vias and/or openings 34therein. The vias/openings 34 are formed at positions corresponding tothe metalized circuits/connection pads 16 formed on semiconductor device12, so as to expose the circuits/connection pads 16. According to oneembodiment of the invention, the vias/openings 34 are formed through thefirst and second passivation layers 22, 30, base dielectric laminate 42,and dielectric film 38 by way of a laser ablation or laser drillingprocess that is performed subsequent to application of the layers 22,30, base dielectric laminate 42, and dielectric film 38 ontosemiconductor device 12. According to one embodiment of the invention,the laser ablation is performed using a laser having a 350 nmwavelength, and the adhesive used to form one or all of first and secondpassivation layers 22, 30 and base dielectric layer 42 is formulatedhaving a tailored sensitivity to laser energy at particularly 350 nmwavelength. Alternatively, the vias/openings 34 may be pre-formed insecond passivation layer 30 and/or dielectric laminates 42, 38 by way ofa laser ablation or laser drilling process that is performed prior toapplication thereof onto first passivation layer 22, again using anadhesive having a tailored sensitivity to laser energy at particularly350 nm wavelength. In an embodiment where the vias/openings 34 arepre-drilled through second passivation layer 30 and dielectric laminates42, 38, a separate reactive ion etching (RIE) process may be performedto extend vias/openings 34 down through first passivation layer 22 tocircuits/connection pads 16. According to additional embodiments of theinvention, it is also recognized that vias/openings 34 may be formed byway of other methods, including plasma etching, photo-definition, ormechanical drilling processes.

Formed within each of vias/openings 34 is a metal interconnect 36 thatextends down through vias/openings 34 to circuits/connection pads 16 onthe semiconductor device 12. Metal interconnects 36 thus form directmetallic and electrical connections to circuits/connection pads 16, withthe interconnects being formed in a tightly packed, close arrangement.Metal interconnects 36 are formed by way of applying a metallayer/material, such as via a sputtering or electroplating process, andthen subsequently patterning the applied metal material into metalinterconnects 36 having a desired shape. The metal interconnects 36 areformed by applying a titanium adhesion layer and copper seed layer via asputtering process, followed by electroplating of additional copperthereon to increase a thickness of the metal interconnects 36. As shownin FIG. 1, on surface 20 of semiconductor device 12, the copper platingof metal interconnects 36 extend out from circuits/connection pads 16 ofsemiconductor device 12, through vias/openings 34, and out across theouter surface of second passivation layer 30 out past the edges 24 ofsemiconductor device 12, with the interconnects 36 in the regionextending out past the edges 24 of semiconductor device 12 being formedon the additional laminate sheet of dielectric film 38 secured to basedielectric laminate 42. On surface 18 of semiconductor device 12, thecopper plating of metal interconnects 36 extend out fromcircuits/connection pads 16 of semiconductor device 12, throughvias/openings 34 formed in base dielectric laminate 42 and dielectricfilm 38, and out across the outer surface of dielectric film 38, withthe interconnects 36 extending out past the edges 24 of semiconductordevice 12 on film 38 and on a side of film 38 opposite from theinterconnects 36 formed on surface 20, so as to be electricallyinsulated therefrom.

Beneficially, the structure of semiconductor device package 10 resultsin a package having a high breakdown voltage and low inductance loop.That is, the arrangement of first and second passivation layers 22, 30and interconnects 36 can provide for a high breakdown voltage of 10 kV,with the thickness thereof being controlled so as to also decreaseparasitic inductance between the anode and cathode in the semiconductordevice package 10. The structure of semiconductor device package 10allows for operation thereof at an improved/efficient operatingfrequency, with reduced switching time and improved signal strength forsubsequent signal transmission (e.g., generation of a square wave pulsefor Fourier processing).

Referring to FIGS. 2-10, various process steps for techniques ofmanufacturing semiconductor device package 10 are set forth. As shown inFIG. 2, the build-up process of semiconductor device package 10 beginswith application of a first passivation or dielectric layer 22 onsemiconductor device 12. The first passivation layer 22 is formed aboutsurfaces 18, 20 and edges 24 of the semiconductor device 12, so as tocover the substrate 14 and metalized circuits/connection pads 16 of thesemiconductor device. First passivation layer 22 may be in the form ofan adhesive that is formed according to embodiments of the invention,including embedded materials such as silicon nitride or silicon oxide,that is applied onto semiconductor device 12 so as to have a uniformthickness. According to one embodiment of the invention, firstpassivation layer 22 is applied using plasma enhanced chemical vapordeposition (PECVD) so as to have a thickness in the order of 1-2microns. The first passivation layer 22 thus serves to passivate theedges 24 of semiconductor device 12 as well as protect the surfaces 18,20 of substrate 14 and metalized circuits/connection pads 16.

Referring now to FIG. 3, in a next step of the build-up process, thesemiconductor device 12, with the first passivation layer 22 appliedthereto, is placed into an adhesive layer 40 and accompanying basedielectric layer 42 that is in the form of a lamination/film. As shownin FIG. 3, semiconductor device 12 is placed onto adhesive layer 40 anddielectric layer 42 such that surface 18 thereof is secured to thelayers 40, 42, with the surface 20 of semiconductor device 12 remainingopen. The dielectric layer 42 may be formed of one a plurality ofdielectric materials, such as Kapton®, Ultem®, polytetrafluoroethylene(PTFE), Upilex®, polysulfone materials (e.g., Udel®, Radel®), or anotherpolymer film, such as a liquid crystal polymer (LCP) or a polyimidematerial. According to an embodiment of the invention, dielectric layer42 is formed using an epoxy resin that is cured using an amine-imidehardener that is described below in FIG. 14. Upon placement ofsemiconductor device 12 onto adhesive layer 40 and base dielectriclamination 42, the adhesive 40 is cured to secure the semiconductordevice 12 on the dielectric lamination 42.

The build-up process continues with application of another dielectric orpassivation layer (i.e., second passivation layer) onto surface 20 andedges 24 of semiconductor device 12. As shown and described below inFIGS. 4-7, it is recognized that such a dielectric layer may be appliedaccording to one of several application processes, such as by way ofapplication of a pre-formed laminate sheet or film layer of dielectricmaterial or by way of application of a liquid dielectric material via aspray coating application, a molding process, or a selective depositionprocess (i.e., “direct writing”).

Referring to FIGS. 4A-4C, dielectric material 44 is applied over surface20 and edges 24 of semiconductor device 12, with an adhesive layer 46(e.g., B-staged, tacky adhesive) included therebetween to secure thesheet of dielectric material 44 to semiconductor device 12. As shown inFIG. 4A, the thickness of dielectric sheet 44 is greater than that offirst passivation layer 22, with the thickness of dielectric sheet 44being determined and controlled based on the dielectric breakdownstrength needed for semiconductor device 12. In general, the thicknessof dielectric sheet 44 will be in the range of around 10-50 microns forevery 1 kV of dielectric breakdown strength needed. According to oneembodiment, in lieu of dielectric sheet 44 and adhesive layer 46, anepoxy or encapsulant is provided that includes a composition and methodof preparing that include embodiments of the invention.

As shown in FIG. 4A, when dielectric material 44 is applied over surface20 and edges 24 of semiconductor device 12 in the form of a laminatesheet, a space or void 48 may be left adjacent the edges 24 ofsemiconductor device 12, which is termed “tenting.” This void 48 isfilled in a next step of the build-up process, as shown in FIG. 4B, withan epoxy or polyimide material 50 that is subsequently cured, whereinepoxy or polyimide material 50 is an epoxy or encapsulant that includesa composition and method of preparing that include embodiments of theinvention. The void 48 is filled from one end with the epoxy/polyimide50, with a vent hole (not shown) being provided at the other end to letout air. It is recognized that if no tenting is seen, then the stepillustrated at FIG. 4B would not be needed.

Referring now to FIG. 4C, additional laminate sheets of dielectricmaterial 52 may be applied over surface 20 and edges 24 of semiconductordevice 12 depending on the electrical requirements of semiconductordevice package 10 (i.e., to further increase the dielectric strength),or additional layers may be provided thereto (in lieu of material 52)using an epoxy or encapsulant that includes a composition and method ofpreparing that include embodiments of the invention. Thus, additionaldielectric material 52 may be positioned on top of the dielectric sheet44 (with an adhesive layer 54 in an embodiment wherein material 52 is asheet) included therebetween to secure the sheets 44, 52 together. Whilenot shown in FIG. 4C, yet still additional sheets or other dielectricmaterials may be added over surface 20 of semiconductor device 12 asneeded.

Referring now to FIG. 5, according to another embodiment of theinvention, a liquid dielectric material 41 is applied over surface 20and edges 24 of semiconductor device 12 via a spray coating application.The liquid dielectric material is formed, according to one embodiment,using an epoxy resin that is cured using an amine-imide hardener that isdescribed below in FIG. 14. After forming, the liquid dielectricmaterial is sprayed onto semiconductor device 12 such that a dielectriclayer 58 is formed having a thickness greater than that of firstpassivation layer 22, with the thickness of dielectric layer 58 beingdetermined and controlled based on the dielectric breakdown strengthneeded for semiconductor device 12. As set forth above, the thickness ofdielectric layer 58 will be in the range of around 10-50 microns forevery 1 kV of dielectric breakdown strength needed. Depending on thedesired thickness and geometry of the dielectric layer 58, multiplespray coating steps may need to be performed.

Referring now to FIGS. 6A-6C, according to another embodiment of theinvention, a liquid dielectric material is applied over surface 20 andedges 24 of semiconductor device 12 using a mold to control a shape andthickness of a resulting dielectric layer. As shown in FIG. 6A,semiconductor device 12 and dielectric layer 42 are flipped over suchthat semiconductor device 12 is pointed downward. The semiconductordevice 12 is then placed into a mold 60 positioned therebelow, with thesemiconductor device 12 being held in place within mold 60 by, forexample, a protrusion 62 formed in the center of mold 60, and such thata space is formed between the semiconductor device 12 and the mold 60.Exact positioning of the semiconductor device 12 within mold 60 may beprovided by a pin align mechanism (not shown), for example. In a nextstep, and as shown in FIG. 6B, the mold 60 is filled with a liquiddielectric material 64, such as an epoxy or polyimide that is formedaccording to embodiments of the invention and described below withrespect to FIG. 14, with the liquid being injected through a fill port(not shown) provided in the mold and into the space between thesemiconductor device 12 and the mold 60. A vent port (not shown) is alsoprovided in the mold to enable injection of the dielectric material 64.Upon filling of the mold 60 with the liquid dielectric material 64, thedielectric is cured and the mold removed, as shown in FIG. 6C, to form afinished dielectric layer 66 over the surface 20 and edges 24 ofsemiconductor device 12. As mold 60 is constructed of Teflon® or asimilar material, the dielectric layer 64 should not stick to the mold60 when removing semiconductor device 12 therefrom.

Referring now to FIG. 7, according to still another embodiment of theinvention, a liquid dielectric material 45 is applied over surface 20and edges 24 of semiconductor device 12 by way of a selective depositionprocess, or a “direct write” process. In direct writing of thedielectric material 45 onto the semiconductor device 12, dielectricmaterial 45 is dispensed using a programmable dispensing tool (notshown) that deposits lines or dots 70 of the dielectric material inliquid form. For example, the programmable dispensing tool may be in theform of an inkjet printing-type device that selectively deposits linesor dots 70 of dielectric material 45 in liquid form. The lines/dots 70are drawn to obtain the necessary coverage of the semiconductor device12 and can be applied in multiple layers to obtain the necessarygeometry and thickness for the dielectric material. The appliedlines/dots 70 of dielectric material are then cured to complete thepassivation.

Referring now to FIG. 8, upon application of the second dielectric orpassivation layer (generally designated henceforth as 30) over surface20 and edges 24 of semiconductor device 12 via one of the techniquesshown and described in the embodiments of FIGS. 4-7, the build-upprocess of semiconductor device package 10 may continue with an ablationof the second passivation layer 30. That is, it is recognized that insome cases the exact desired geometry/thickness of the secondpassivation layer 30 may not be obtained and slight modifications to theprofile may need to be performed. One method that is used is laserablation, or a similar method, to ablate away excess material to obtainthe necessary profile of the passivation layer 30. As such, among themany beneficial properties derived from formulation of anepoxy/encapsulant according to the invention, as will be furtherdescribed below, it is desirable that passivation layer 30 be ablatablewith a laser. A typical laser for ablating includes a coherent lightbeam having a 350 nm wavelength. Thus, according to the invention and aswill be described, an epoxy/encapsulant for passivation layers describedherein, in this case second passivation layer 30, is formulated thatincludes a targeted sensitivity to laser ablation at particularly 350nm. That is, in the above chip assemblies described, where a highdielectric strength material is desired and where laser ablation may beperformed to form a via, embodiments of the invention may be used suchthat the material has a specific sensitivity for ablation at 350 nm. Asshown in FIG. 8, the passivation layer 30 is shown as having atrapezoidal shape so as to match the trapezoidal shape of semiconductordevice 12; however, it is recognized that other shapes andconfigurations for both passivation layer 30 and semiconductor device 12are envisioned, such as a rectangular shape, for example. Themodification of the thickness and/or geometry of second passivationlayer 30 using laser ablation or another method can be performed for anyof the dielectric material application methods set forth above,including the laminate application (FIGS. 4A-4C), spray coatingapplication (FIG. 5), molding application (FIGS. 6A-6C), or directwriting application (FIG. 7). Thus, any of the dielectric materialsdiscussed above may be prepared according to embodiments of theinvention, and in particular for applications where it is desirable tolaser ablate excess material. If, however, the desired geometry of thesecond passivation layer 30 is obtained upon an initial application ofthe dielectric material onto semiconductor device 12, such as may beenvisioned especially using the molding application or direct writingapplication, it is recognized that ablating of the second passivationlayer 30 to alter the thickness and geometry thereof may be forgone.

As further shown in FIG. 8, the semiconductor device 12 is “trimmed”such that a portion of any dielectric laminations (and accompanyingadhesive layers) extending out past a desired profile of secondpassivation layer 30 along edges 24 of the semiconductor device 12 isremoved. According to that shown in FIG. 8, a portion of base dielectriclamination 42 and adhesive layer 40 are trimmed from semiconductordevice 12, such as by way of a laser ablation, for example, and using adielectric material as described according to embodiments of theinvention. It is recognized, however, that additional dielectriclaminations extending out past a desired profile of second passivationlayer 30 along edges 24 of the semiconductor device 12 could also betrimmed, such as dielectric lamination 52 (and adhesive layer 56) shownin FIG. 4C, for example. Similar to the removal of any excess materialfrom the dielectric material formed about surface 20 and edges 24 ofsemiconductor device 12, the trimming of any dielectric laminations 42extending out past a desired profile of second passivation layer 30along edges 24 of the semiconductor device 12 may be performed so asachieve a desired shape of the remaining portion of dielectric layer 42attached to semiconductor device 12. Thus, in the embodiment of FIG. 8,the trimming of semiconductor device 12 out from base dielectriclamination 42 is performed at an angle so as to maintain an overalltrapezoidal shape of the second passivation layer 30 about semiconductordevice 12.

Referring now to FIG. 9, upon shaping of second passivation layer 30 andtrimming of the semiconductor device 12 out from base dielectric layer42, a passivated semiconductor device 72 is thus formed. The passivatedsemiconductor device 72 is subsequently attached to a dielectric sheet(e.g., polyimide sheet) 74 via an adhesive layer 76. As shown in FIG. 9,dielectric sheet 74 includes a window 78 opening pre-cut therein thatgenerally corresponds in size to semiconductor device 12. It isrecognized, however, that dielectric sheet 74 could also be in the formof a continuous sheet (i.e., no window pre-cut therein), and that awindow could subsequently be formed therein after placement ofpassivated semiconductor device 72 on the dielectric sheet 74.

Upon securing passivated semiconductor device 72 to dielectric sheet 74,the build-up process of semiconductor device package 10 continues withthe patterning and interconnection steps illustrated in FIGS. 10-13.With regard to these build-up steps, it is recognized that the techniqueused to apply second passivation layer 30 over surface 20 and edges 24of semiconductor device 12 will determine the exact steps requiredregarding patterning the passivation layer 30 and making electricalinterconnections to the top and bottom of the semiconductor device 12.Such variations in the exact build-up process steps employed in thepatterning and interconnecting steps are addressed below

Referring to FIG. 10, vias and contact areas (i.e., openings) 34 areformed in first and second passivation layers 22, 30 so as to provideaccess to circuits/connection pads 16 of semiconductor device 12. Thevias/openings 34 are formed at positions corresponding tocircuits/connection pads 16 on semiconductor device 12, with thevias/openings 34 being formed down to the first passivation layer 22formed over those circuits/connection pads 16. According to embodimentsof the invention, the vias/openings 34 may be formed by way of a laserablation or laser drilling process, plasma etching, photo-definition, ormechanical drilling processes. In an embodiment of the invention wheresecond passivation layer 30 is applied in the form of one or moredielectric laminations/sheets, such as sheets 44, 52 shown in FIGS.4A-4C, vias/openings 34 may be mechanically drilled through thedielectric layer(s) and adhesive layer(s) applied over semiconductordevice 12. In an embodiment of the invention where the secondpassivation layer 30 is applied via spray coating, direct writing, ormolding, such as in FIGS. 5-7, vias/openings 34 may be formed in thepassivation layer 30 in the regions that require interconnection to thedevice 12 using a laser ablation or laser drilling, and using adielectric material that includes a composition and method ofpreparation according to embodiments of the invention. It is recognized,however, that certain methods of applying second passivation layer 30may negate the need for subsequent ablating or drilling of vias/opening34 therein. For example, for application of dielectric materialemploying a mold or direct writing technique, one or more vias/openings34 may already be formed in second passivation layer 30.

In a next step of the patterning/interconnect process, and as shown inFIG. 11, the vias/opening 34 are further extended down to thecircuits/connection pads 16 on semiconductor device 12 by removing thefirst passivation layer 22 that is present over the circuits/connectionpads 16 at the locations corresponding to vias/opening 34. Firstpassivation layer 22 adjacent metal circuits and connection pads 16 ofsemiconductor device 12 may be removed by way of a reactive ion etching(RIE) process, although it is envisioned that other suitable techniquesmay also be employed. Upon extending of vias/opening 34 by way ofremoving of first passivation layer 22, the circuits/connection pads 16of semiconductor device 12 are exposed so as to provide for anelectrical interconnection to be made to those circuits/connection pads.

Upon completion of the formation of vias/opening 34 down tocircuits/connection pads 16, the vias/opening 34 are cleaned (such asthrough an RIE desoot process) and subsequently metalized to forminterconnects 36, as shown in FIG. 12. The metal interconnects 36 aretypically formed through a combination of sputtering and electroplatingapplications. For example, a titanium adhesion layer and copper seedlayer may first be applied via a sputtering process, followed by anelectroplating process that increases a thickness of the copper to adesired level. The applied metal material is then subsequently patternedinto metal interconnects 36 having a desired shape. As shown in FIG. 12,metal interconnects 36 form direct metallic and electrical connectionsto circuits/connection pads 16 on semiconductor device 12. The metalinterconnects 36 extend out from circuits and/or connection pads 16 ofsemiconductor device 12, through vias/opening 34, and out acrossopposing surfaces 18, of semiconductor device 12. The metalinterconnects 36 further extend out past the edges 24 of semiconductordevice 12 on opposing surfaces of dielectric sheet 74, such as in theform of copper plating on the dielectric sheet 74.

According to an embodiment of the invention where semiconductor device12 is in the form of an optical diode (i.e., diode with light-basedswitching), a further patterning step is performed to remove anadditional portion 80 of base dielectric layer 42. As shown in FIG. 13,portion 80 of base dielectric sheet 42 and adhesive layer 40 are ablatedoff of surface 18 of passivated semiconductor device 72, with a metalcircuit/contact 16 serving as a backstop or mask for the ablating. Anopen window 82 is thus formed on surface 18 of passivated semiconductordevice 72 that allows light to reach the optical diode 12. In such anembodiment, it is recognized that first passivation layer 22 would becomposed of an optically clear and anti-reflective material that permitslight to pass there through, while still offering protection of opticalwindow 82 of the semiconductor device package 10.

Described throughout the aforementioned figures, including thesemiconductor device package of FIG. 1 and the various stages ofmanufacturing and build-up of the device in FIGS. 2-13, a dielectriclayer or passivation layer is provided that includes a compositionaccording to an embodiment of the invention, and a method of forming thecomposition according to another embodiment of the invention.

Thus, an adhesive having the following beneficial properties isdisclosed, according to an embodiment of the invention:

-   -   low viscosity to enable filling tight tolerances in a mold and        also to allow spin coating onto a dielectric film for the method        when it is used as a lamination adhesive;    -   ability to “partial cure” the adhesive when spun coated onto a        film for lamination and thus control its flow properties during        lamination and thereby achieve the desired dielectric        thicknesses on a chip perimeter;    -   low surface tension to help void free encapsulation—both molding        and lamination, where “wetting” the surface helps eliminate        voids and provides a smoother spin coated films for lamination        (no pullback, fish-eyes—this is also useful when the material is        used as an underfill for components mounted on dielectric films        (chip on flex), or where an ability to wet (underfill) and cure        with low stress allows components on flex to be encapsulated        without voids and warpage);    -   low stress (i.e., minimal shrinkage on cure and low storage        modulus) to prevent warpage of a large chip—useful for molding,        lamination, underfill, and the like;    -   reasonable (>1 hour) working pot life once the resin and        hardener are mixed to allow degassing and application into the        mold and/or spin coating on a film and subsequent lamination;    -   ability to substantially cure (or gel) at room or low        temperature (<60° C.) (this enables void free molding and/or        lamination because higher temperatures increase vapor pressures        of the adhesive components which can cause voids, and once a        “substantial” cure is complete, high temperature can be applied        to complete the cure without concern for void formation and/or        additional flow out);    -   sufficient absorption at ˜350 nm to allow laser ablation of        material from selected areas of the chip;    -   a glass transition temperature (T_(g)) high enough to prevent        swelling and/or liquefying of the epoxy during ablation; and    -   dielectric properties to withstand a high voltage operating        environment needed for high frequency/low loss operation.

Low molecular weight, amine terminated polyimide oligomers aresynthesized, degassed and added to cycloaliphatic amine compounds toobtain a liquid amine curing agent with specific amine equivalentweight, according to the invention. This material, when combined with aliquid epoxy resin, forms a low viscosity solution useful for chipencapsulation, lamination adhesive, and the like. This blend will gelwithin a few hours at room temperature and completely cure upon exposureto heat. The disclosed polyimide content epoxy blend increases thematerial's absorption at 350 nm, allowing clean laser ablationpatterning with an laser having a 350 nm wavelength.

The amine hardener is a blend of trioxdiamine,diaminodicyclohexylmethane, toluene diamine and bisphenol-A dianhydride.It is made by adding the dianhydride into an excess of the diamineblend, and heating to remove water of imidization. The final productcontains low molecular weight (MW) amine terminated imide oligomers andsome free diamines. This provides a hardener that is strongly absorbingdue to the imide linkages present, but still has a viscosity low enoughto be mixed with an epoxy resin at room temperature. The imide oligomersalso improve the thermal and electrical properties of the final curedblend as well as reduce shrinkage on cure.

The epoxy resin used with the amine hardener is, according to oneembodiment, a diepoxy such as liquid cycloaliphatic. In one embodimentthe cycloaliphatic is Araldite® CY184 (Araldite is a registeredtrademark of Huntsman Advanced Materials of Switzerland), optionallycombined with bisphenol-A and bisphenol-F resins. Such products aretypically distilled prior to use to ensure high purity (low halogencontent) and because they are glycidyl epoxies, all react well withamine hardeners.

Also included during the final mixing of the epoxy encapsulant is asmall amount of Zonyl® FSN-100 nonionic fluorosurfactant (Zonyl is aregistered trademark of Du Pont, a Delaware Corporation). This materiallowers surface tension at interfaces between the epoxy blend andsubstrate, providing better wetting and smoother coatings.

Technique 100 below describe how this adhesive is made according to anembodiment of the invention, referring to FIG. 14:

Into a round bottom reaction flask is added the following reactants:

-   -   80 grams—4,7,10-Trioxatridecane-1,13-diamine (also referred to        as trioxdiamine, MW=220 grams/mole) (step 102);    -   80 grams—Bis (p-aminocyclohexyl) methane (also referred to as        diaminodicyclohexylmethane or bis-PACM, MW=210 grams/mole) (step        104);    -   1.0 gram—2,4-Diaminotoluene (also referred to as toluene diamine        or TDI, MW=122 grams/mol) (step 106); and    -   32 grams—4,4-bisphenol-A dianhydride (also referred to as        bisphenol-A dianhydride or BPADA, MW=520 grams/mole) (step 108).

At step 110 The mixture is heated under a partial vacuum (−50 torr) withstirring to enable condensation imidization reaction of the anhydridegroups with amine resulting in the formation of water. During the courseof approximately 1 hour of heating, the water of imidization isdistilled 112 from the reactants along with some of the diaminereactants at a temperature ranging from approximately 160° C. to 190° C.About 66 grams of distillate is obtained, consisting of 2.2 grams waterand 32 grams each of tri-oxdiamine and bis-PACM. This distillate mixtureis discarded, resulting in an amine-imide mixture 114.

Into the amine-imide mixture is added the following material:

-   -   20 gr—3,3′-Dimethyl-4,4′diamino-dicyclohexylmethane (also        referred to as dimethyl bis-PACM, MW=238 grams/mole) (step 116).

After blending, the amine hardener mixture is complete 118 and resultsin a transparent, yellow colored liquid having a viscosity of about10,000 centipoise at room temperature. Referring to FIG. 15, an epoxyadhesive and/or molding encapsulant is prepared 200 with this aminemixture using the following formulation:

-   -   2.2 grams—amine/imide hardener (prepared as described above and        completed at step 118) (step 202);    -   5.0 grams—Diglycidyl 1,2-cyclohexanedicarboxylate (also referred        to as a cycloaliphatic diepoxy, MW=284 grams/mole) (step 204);        and    -   0.02 gram Zonyl® FSN-100 fluorosurfactant. Zonyl® FSN-100 is a        water-soluble, ethoxylated nonionic flurosurfactant that        contains no solvent. (step 206)

The above materials are mixed or blended 208 together in a small mixingcontainer, poured into a dispense tube and degassed 210 for about 30minutes under vacuum at 40° C. The resultant blend, when cooled to roomtemperature, has a viscosity of about 2500 centipoise and is stable forabout 1 hour for use 212 before it slowly begins increasing viscositydue to cure. Final cure of the epoxy blend is generally accomplishedwith a 15 hour room temperature cure followed by heating to 180° C. over2 hours and dwelling at temperature for 30 minutes. Cured epoxy has aglass transition temperature (T_(g)) of 80° C. measured by adifferential scanning calorimetry.

The composition can be modified for increased glass transitiontemperature (Tg) (adding more 4,4-bisphenol-A dianhydride and/or Bis(p-aminocyclohexyl) methane)), increased absorbance (adding morediaminotoluene), lower viscosity (increased4,7,10-Trioxatridecane-1,13-diamine) and quicker cure by addingaccelerators such as tris(dimethylaminomethyl) phenol. Also, the epoxyportion can be modified by replacing part or all of the liquid epoxyresin with resins or combinations of resins such as bisphenol-A diepoxy,bisphenol-F diepoxy, epoxy novolacs, glycidyl ether diepoxies andothers. As known in the art, bisphenol and novolac epoxy resins are notcycloaliphatic, but aromatic containing resins, and glycidyl etherresins are aliphatic and are not cyclo aliphatic. The object is toobtain a liquid epoxy blend which can be used as both an encapsulant,underfill and adhesive which, upon mixing and cure provides all therequirement listed above.

According to one embodiment of the invention, an adhesive includes anepoxy resin and a hardener. The hardener includes trioxdiamine,diaminodicyclohexylmethane, toluene diamine, and bisphenol-Adianhydride.

According to another embodiment of the invention, a method of preparingan adhesive includes mixing together a plurality of reactants to form ahardener, the reactants comprising trioxdiamine,diaminodicyclohexylmethane, toluene diamine, and bisphenol-Adianhydride, mixing the hardener with an epoxy resin to form an uncuredadhesive mixture, and curing the uncured adhesive mixture.

According to yet another embodiment of the invention, a method offorming a semiconductor device package includes positioning asemiconductor device against a material to form a space between asurface of the semiconductor device and the material, mixing together aplurality of reactants to form a hardener, the reactants comprisingtrioxdiamine, diaminodicyclohexylmethane, toluene diamine, andbisphenol-A dianhydride, mixing the hardener with an epoxy resin to forman uncured adhesive mixture, placing the uncured adhesive mixture intothe space, and curing the uncured adhesive mixture.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

What is claimed is:
 1. An adhesive comprising: an epoxy resin; and ahardener comprising: trioxdiamine; diaminodicyclohexylmethane; toluenediamine; and bisphenol-A dianhydride.
 2. The adhesive of claim 1 furthercomprising a water-soluble, ethoxylated surfactant.
 3. The adhesive ofclaim 1 wherein the epoxy resin comprises a liquid diepoxy.
 4. Theadhesive of claim 3 wherein the liquid diepoxy comprises one of acycloaliphatic epoxy, a bisphenol-A epoxy resin, a bisphenol-F epoxyresin, an epoxy novolac, and a glycidyl ether epoxy resin.
 5. Theadhesive of claim 1 comprising an accelerator comprisingtris(dimethylaminomethyl) phenol.
 6. A method of preparing an adhesivecomprising: mixing together a plurality of reactants to form a hardener,the reactants comprising trioxdiamine, diaminodicyclohexylmethane,toluene diamine, and bisphenol-A dianhydride; mixing the hardener withan epoxy resin to form an uncured adhesive mixture; and curing theuncured adhesive mixture.
 7. The method of claim 6 comprising mixing awater-soluble, ethoxylated surfactant with the uncured adhesive mixture.8. The method of claim 6 wherein mixing together the plurality ofreactants comprises mixing the trioxdiamine, thediaminodicyclohexylmethane, the toluene diamine, and the bisphenol-Adianhydride in approximate respective amounts, measured by mass, of80:80:1:32.
 9. The method of claim 6 comprising heating the hardenerunder partial vacuum prior to mixing the hardener with the epoxy resin.10. The method of claim 6 wherein mixing together the plurality ofreactants to form the hardener comprises first mixing together thetrioxdiamine, the diaminodicyclohexylmethane, and the toluene diamine toform a diamine blend, then adding the bisphenol-A dianhydride into anexcess of the diamine blend.
 11. The method of claim 10 comprisingheating the hardener after the bisphenol-A dianhydride has been addedinto the excess of the diamine blend to remove water of imidization thatresults from adding the bisphenol-A dianhydride to the diamine blend.12. The method of claim 11 wherein heating the hardener comprisesheating the hardener to between 160° C. and 190° C.
 13. The method ofclaim 6 wherein mixing the hardener with the epoxy resin comprisesmixing the hardener with a liquid diepoxy.
 14. The method of claim 13comprising mixing the liquid diepoxy with one of a cycloaliphatic epoxy,bisphenol-A epoxy resin, a bisphenol-F epoxy resin, an epoxy novolac,and a glycidyl ether epoxy resin prior to mixing the hardener with theepoxy resin.
 15. The method of claim 6 comprising adding an acceleratorcomprising tris(dimethylaminomethyl) phenol to the uncured adhesivemixture.
 16. The method of claim 6 comprising ablating the adhesiveafter curing using a laser having approximately a 350 nm wavelength. 17.A method of forming a semiconductor device package comprising:positioning a semiconductor device against a material to form a spacebetween a surface of the semiconductor device and the material; mixingtogether a plurality of reactants to form a hardener, the reactantscomprising trioxdiamine, diaminodicyclohexylmethane, toluene diamine,and bisphenol-A dianhydride; mixing the hardener with an epoxy resin toform an uncured adhesive mixture; placing the uncured adhesive mixtureinto the space; and curing the uncured adhesive mixture.
 18. The methodof claim 17 wherein mixing the hardener with the epoxy resin comprisesmixing the hardener with a liquid cycloaliphatic diepoxy.
 19. The methodof claim 17 comprising mixing a water-soluble, ethoxylated surfactantwith the uncured adhesive mixture.
 20. The method of claim 17 whereinmixing together the plurality of reactants comprises mixing thetrioxdiamine, the diaminodicyclohexylmethane, the toluene diamine, andthe bisphenol-A dianhydride in approximate respective amounts, measuredby mass, of 80:80:1:32.